In Germany, the X121e / AMD E450 is currently available dirt cheap at around 300 EUR (ca. 400 USD). Now, I wonder: Is it possible to later upgrade it with an mSATA SSD, to be used in addition to the conventional HDD?

Price wise, the alternative could be an Edge E325 or an Edge E135, both with AMD CPUs. But that would raise the same question, and I assume that Edge Thinkpads are not as rugged.